Shahrasti thana with a population of around 200,000 is located about 40 kilometers from Matlab, and is well connected with Comilla, Chandpur and Dhaka by road. According to BAMWSP (Bangladesh Arsenic Mitigation Water Supply Project), subsoil water in Shahrasti Thana is heavily contaminated with arsenic; about 99% of the tube wells are reported to have been contaminated (50 microgram/L). BAMWSP and DGHS have already identified 3000 patients with skin lesions consistent with arsenic toxicity, and represent the area with the second highest number of arsenic-induced skin lesions in Bangladesh. In collaboration with ICDDR,B, the University Chicago and Columbia University are jointly conducting a large longitudinal surveillance and clinical trial on patients with arsenic induced skin lesion. The aim of this large study is to reduce skin cancer by evaluating clinical as well biochemical markers. We plan to study responses of children in these sites to Dukoral using the infrastructure and facilities from the ongoing studies . The immunogenicity studies will be carried out as described earlier. We plan to immunize 102 children aged 2-5 years with two doses of Dukoral at an interval of 14 days. Equal numbers of children will be studied in an area known to have low levels of arsenic, in Mirpur field site in Dhaka city . This will be the first study to compare immune responses to a mucosal vaccine in an arsenic prone and arsenic low area.